1. Field
This patent specification relates to allocating commingled oil production. More particularly, this patent specification relates to methods and systems for allocating commingled oil production in real-time based on measurements made at or near the wellsite.
2. Background
Commingling is a common practice in the oil industry for sharing facilities and equipment to reduce costs. Examples of commingling include: producing two or more reservoirs through a single tubing string, mixing gas/oil/water from several wells in a single separator tank, and using a single pipeline for transporting production from several fields. Crude oils originating from different producing zones, wells, platforms or fields are mixed through commingling operations. See, Hwang R. J., Baskin D. K., Teerman S. C., Allocation of commingled pipeline oils to field production, Organic Geochemistry, vol. 31 pp 1463-1474, 2000 (hereinafter “Hwang et al., 2000”).
There are several reasons that accurate assessment of the individual field contributions may be desirable or necessary. For example, it may be desirable to have an accurate assessment of the amount of producible oil or gas (See, Peters K. E., Fowler M. G., Application of Petroleum Geochemistry to Exploration and Reservoir Management, Organic Geochemistry, vol. 33, pp 5-36, 2002), and to effectively plan future directions, so as to avoid costly exploration failures (See, International Patent Application No. WO 2008/002345). Another example is the matching of current allocation data with historical data to assess production and plan remedial operations on the well (e.g. pipeline leaks, cement bond failures, non productive zones), to use in a workflow leading to critical management and investment decisions (See, International Patent Application No. WO 2008/002345; and Kaufman R. L., Ahmed A. S., Hempkins W. B., A New Technique for the Analysis of Commingled Oils and its Application to Production Allocation Calculations, Organic Geochemistry vol. 31 pp 1463-1474, 2000 (hereinafter “Kaufmann et al. 1990”)). Finally, petroleum sales value and tax dues often depends on the quality of oil, varying ownership and tax regimes among different zones or neighboring fields (Hwang et al., 2000).
Back-allocation of commingled production or transport is conventionally being carried out though wireline logging (e.g. Production Logging Tool (PLT), Reservoir Sampling with MDT/DST), and production metering coupled with modeling and simulation. Recently, gas chromatographic analysis coupled with matrix mathematics has been employed to back allocate commingled pipeline crude from multiple contributing fields. In most cases, the use fluid geochemistry is used as an accompaniment to the more traditional techniques mentioned above.
Several studies discuss the potential of using gas chromatograms as a means of differentiating and allocating hydrocarbon fluids. For discussions of employing gas chromatography analysis to perform zonal and well-to-well allocation, see: Kaufmann et al. 1990, Bazan L. W., The Allocation of Gas Well Production Data using Isotope Analysis, SPE 40032, Gas Technology Symposium, Calgary, Canada, March 1998; Hwang et al 2000; Milkov A. V., Goebel E., Dzou L., Fisher D. A., Kutch A., McCaslin N., Bergman D. F., Compartmentalization and Time-lapse Geochemical Reservoir Surveillance of the Horn Mountain oil field, Deep-water Gulf of Mexico, AAPG Bulletin vol. 91, No 6 pp 847-876, 2007; Wen Z., Zhu D., Tang Y., Li Y., Zhang G., The application of gas chromatography fingerprint technique in calculating oil production allocation of single layer in the commingled well, Chinese Journal of Geochemistry, Vol. 24 No. 3, 2005; McCaffrey M. A., Legarre H. A., Johnson S. J., Using Biomarkers to improve Heavy Oil Reservoir Management: An example from the Cymric field Kern Count, Calif., AAPG Bulletin, Vol. 80 No. 6 pp 898-913, June 1996; and Nengkoda A, Widojo S, Mandhari M. S., Hinai Z, The Effectiveness of Geochemical Technique for Evaluation of Commingled Reservoir: A Case Study, SPE 109169, Asia Pacific Oil & Gas Conference and Exhibition, Jakarta, Indonesia, November 2007.
However, such gas chromatography based analyses use relatively complex equipment located in a laboratory in a location remote from the wellsite. Therefore the results are delayed and can be affected by changes in and possible contamination of the sample during transportation. Furthermore, complex gas chromatographic techniques are inherently prone to human operator errors.
Reyes, M V. Crude Oil Fingerprinting by the Total Scanning Fluorescence Technique, SPE 26943, 1993, Eastern Regional Conference & Exhibition 1993, discusses an application of total scanning fluorescence for crude oil fingerprinting, but does not discuss applying the techniques to the problem of production allocation. The technique relies on the detection of wide range of poly-aromatic hydrocarbon compounds (PAH) as well as the mono-ring aromatics.
Pasadakis, N., Chamilaki E., Varotsis N., Method measures commingled production, pipeline components, Oil & Gas Journal pp 46-47, Jan. 3, 2000 discusses the use Fourier Transform-Infrared Spectroscopy in identifying volumetric cuts in a three-oil mixture sample. FT-IR analyses use differences in the IR oil spectra in the region of about 3,000 cm−1. Relative to other methods, analysis requires less time with the quantitative determination absolute error was found to be less than 2%. The analysis seems to have been performed in a lab, and there is no suggestion that the process can be performed real-time or at the wellsite.
Permanyer A., Rebufa C., Kister J., Reservoir compartmentalization assessment by using FTIR spectroscopy, Journal of Petroleum Science & Engineering vol. 58 pp 464-471, 2007 Permanyer et al (2007), discusses, on the other hand, the application of FT-IR spectroscopy for reservoir compartmentalization assessment and stress the complementary benefits that the techniques provide to conventional GC analysis.